Methods of forming an electrical contact to semiconductive material

ABSTRACT

A method of forming an electrical contact to semiconductive material includes forming an insulative layer over a contact area of semiconductive material. A contact opening is etched through the insulative layer to the semiconductive material contact area. Such etching changes an outer portion of the semiconductive material exposed by the etching. The change is typically in the form of modifying crystalline structure of only an outer portion from that existing prior to the etch. The changed outer portion of the semiconductive material is etched substantially selective relative to semiconductive material therebeneath which is unchanged. The preferred etching chemistry is a tetramethyl ammonium hydroxidde solution. A conductive material within the contact opening is formed in electrical connection with the semiconductive material. In another aspect, the changed outer portion is etched with a basic solution regardless of selectivity in the etch relative to semiconductive material therebeneath which is unchanged by the contact opening etch. The preferred conductive material is conductively doped semiconductive material which is formed in the contact opening to be in contact with semiconductive material which is unchanged. Further, the conductive material within the contact opening is preferably void of any silicide material.

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. patentapplication Ser. No. 032,261 U.S. Pat. No. 6,281,131, filed Feb. 27,1998 entitled “Methods of Forming Electrical Contacts”, naming Terry L.Gilton, Casey Kurth, Russ Meyer and Phillip G. Wald as inventors, thedisclosure of which is incorporated by reference.

TECHNICAL FIELD

This invention relates generally to methods of forming electricalcontacts to semiconductive material.

BACKGROUND OF THE INVENTION

In semiconductor circuitry fabrication, electrical connections orcontacts are commonly made between conductive lines and conductivediffusion areas formed within a semiconductive substrate. In the contextof this document, the term “semiconductive substrate” is defined to meanany construction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above. Such electrical contacts are typically accomplished byinitially etching a contact opening through insulative material over aconductive diffusion region comprising highly doped semiconductivematerial to which electrical connection is desired. Conductive material,such as conductively doped semiconductive material, is thereafter formedwithin the contact opening in electrical connection with the diffusionregion within the semiconductive substrate. The conductive contactfilling material can then either be planarized or, if deposited to asufficient thickness, patterned into a conductive line or other desiredelectronic component.

One problem associated with such connections is exemplified in FIG. 1.There illustrated is a semiconductor wafer fragment 10 comprised of a p-doped monocrystalline silicon substrate having a pair of conductive gatelines 14 and 16 formed thereover. Source/drain diffusion regions 18, 20,and 22, constituting n+ dopant, are formed within substrate 12 to formfield effect transistors. In this example, ii electrical connection withan overlying conductive line is desired to be made with respect todiffusion region 20.

An insulating layer 24 is formed over substrate 12 and gates 14 and 16,and is subsequently planarized. A contact opening 26 is then patternedand formed, typically by dry etching, through insulating layer 24 overdiffusion region 20. Such has the effect of roughening or otherwisedamaging the outer surface of silicon substrate 12 within diffusionregion 20 upon outward exposure thereof. This also undesirably has atendency to change an outer portion 28 of the semiconductive material ofsubstrate 12 exposed by the contact etching. This change typicallymanifests itself in a modified crystalline structure of the siliconmaterial of substrate 12. Subsequently, a buried contact ion implantregion 30 is formed into and through region 28 within diffusion region20. Implant 30 is provided to achieve enhanced electrical contactbetween diffusion region 20 and a subsequently deposited conductivematerial. The substrate is typically subjected to an anneal in anattempt to repair or overcome the silicon damage caused by both the dryetch forming contact opening 26 and that caused by the implant to formregion 30.

The wafer is subjected to an HF clean for a short period of time toclear any native oxide formed over region 20. A conductive layer 32 isthen formed within contact opening 26 and over insulating layer 24, forexample by depositing or otherwise forming a conductively dopedsemiconductive material such as polysilicon.

Unfortunately, the combined effect of both the changed outer portion 28from the dry etch and the subsequent implant region 30, even with asubsequent anneal, forms a less than desired electrical connectionbetween the diffusion region and conductive material 32, particularlywhere the conductive material within contact opening 26 is essentiallyvoid of any silicide material. It would be desirable to overcome some ofthese drawbacks associated with forming electrical contacts tosemiconductive material.

SUMMARY OF INVENTION

In one aspect of the invention, a method of forming an electricalcontact to semiconductive material includes forming an insulative layerover a contact area of semiconductive material. A contact opening isetched through the insulative layer to the semiconductive materialcontact area. Such etching changes an outer portion of thesemiconductive material exposed by the etching. The change is typicallyin the form of modifying crystalline structure of only an outer portionfrom that existing prior to the etch. The changed outer portion of thesemiconductive material is etched substantially selective relative tosemiconductive material therebeneath which is unchanged. The preferredetching: chemistry is a tetramethyl ammonium hydroxide solution. Aconductive material within the contact opening is formed in electricalconnection with the semiconductive material.

Is In another implementation, the changed outer portion is etched with abasic solution regardless of selectivity in the etch relative tosemiconductive material therebeneath which is unchanged.

The preferred conductive material is conductively doped semiconductivematerial which is formed in the contact opening to be in contact withsemiconductive material which is unchanged. Further, the conductivematerial within the contact opening is preferably void of any silicidematerial.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a cross-sectional view of a prior art semiconductor waferfragment, and is discussed in the “Background” section above.

FIG. 2 is a cross-sectional view of a semiconductor wafer fragment atone process in accordance with the invention.

FIG. 3 is a view of the FIG. 2 wafer fragment at a processing stepsubsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 2 wafer fragment at a processing stepsubsequent to that shown by FIG. 3.

FIG. 5 is a view of the FIG. 2 wafer fragment at a processing stepsubsequent to that shown by FIG. 4

FIG. 6 is a diagrammatic cross-sectional view of an alternate issemiconductor wafer fragment at an alternate processing step inaccordance with the invention.

FIG. 7 is a view of the FIG. 6 wafer fragment at a processing stepsubsequent to that shown by FIG. 6.

FIG. 8 is a view of the FIG. 6 wafer fragment at a processing stepsubsequent to that shown by FIG. 7.

FIG. 9 is a diagrammatic cross-sectional view of another alternateembodiment semiconductor wafer fragment at another alternate processingstep in accordance with the invention.

FIG. 10 is a view of the FIG. 9 wafer fragment at a processing stepsubsequent to that shown by FIG. 9.

FIG. 11 is still another cross-sectional view of an alternate embodimentwafer fragment at an alternate processing step in accordance with theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

FIG. 2 illustrates a semiconductor wafer fragment 40 similar to theprior art depiction of FIG. 1. Like numerals have been utilized whereappropriate, with differences being indicated with different numerals.Diffusion region 20 constitutes a contact area 42 of semiconductivematerial to which electrical contact is desired. Gates 14 and 16 areprovided over substrate 12, with source/drain regions 18, 20 and 22being formed within substrate 12, thus forming desired field effecttransistors. Insulating layer 24 is formed over contact area 42 and thegates and diffusion regions of such field effect transistors.

Referring to FIG. 3, contact opening 26 is etched through insulatinglayer 24 to semiconductive material contact area 42, typically utilizinga suitable dry etch chemistry which is selective to etch silicon dioxiderelative to underlying silicon. An example etch chemistry includesC₂F₅H, CHF₃, and CH₂F₂ in a plasma etcher. Such etching changes an outerportion 28 of the semiconductive material exposed by the contactetching, typically by undesirably modifying the crystal structure of thesilicon lattice within substrate 12, which in this embodiment is anouter portion of source/drain diffusion region 20. Regardless andalternately considered in one implementation, outer portion 28 isprovided to have a different crystalline structure than semiconductivematerial immediately therebeneath whether resulting from the etch, andwhether occurring before or after such etch.

Referring to FIG. 4, and in accordance with but one aspect of theinvention, changed outer portion 28 is etched substantially selectiverelative to semiconductive material therebeneath of diffusion region 20which is unchanged by the contact etching which formed opening 26. Suchouter portion etching preferably comprises wet etching using, forexample, a solution of tetramethyl ammonium hydroxide comprising fromabout 05% to 10% tetramethyl ammonium hydroxide by weight relative todeionized water. Pressure during etching is preferably ambient, with anexample etching temperature being 30° C. In the context of thisdocument, a substantially selective etch is defined by an etch whichetches one material relative to another material at a removal rate of atleast 2:1. Selectivity in this etch using the above example tetramethylammonium hydroxide solution wherein substrate 12 comprisesmonocrystalline silicon and diffusion region 20 constitutes phosphorusdoping to a level of at least 1×10²⁰ ions/cm³ is expected to be 2greater than or equal to 5:1.

In accordance with an alternate implementation, outer portion 28 isetched using some basic solution which etches outer portion 28regardless of selectivity relative to underlying semiconductive materialtherebeneath. Regardless, preferably the etching of the changed outerportion is conducted to etch all exposed changed outer portion material.FIG. 4 illustrates outer portion 28 having been substantially removedfrom source/drain diffusion region 20 of semiconductive substrate 12.

Referring to FIG. 5, conductive material 32 is formed within contactopening 26 in electrical connection with the semiconductive material ofdiffusion region 20. Such material preferably comprises polysilicon orsome other semiconductive material conductively doped to a concentrationof about 1×10²⁰ ions/cm³. Contact opening 26 is thereby preferablyformed to be void of any silicide, with material 32 being in contactwith semiconductive material of diffusion region 20 which is unchangedfrom the contact etching.

An alternate preferred embodiment is described with reference to FIGS.6-8. Like numerals from the FIGS. 2-5 embodiment are utilized whereappropriate, with differences being indicated with different numerals orwith the suffix “a”. Wafer fragment 40 a in FIG. 6 depicts waferfragment 40 of the FIGS. 2-5 embodiment at a step immediately subsequentto that depicted by FIG. 3. Specifically, after contact opening 26 hasbeen formed, a conductivity enhancing impurity is ion implanted intochanged outer portion 28. An example implant is phosphorus at a dose of9×10¹² atoms/cm² and energy of 80 keV. Region 30 is shown as having beenimplanted into and through region 28. Alternately, the implant could beconducted to be shallower, for example to substantially only place theimplanted impurity into the changed outer portion. Further alternately,the implanting can be conducted to place the dopant concentration of theimplant substantially central relative to the thickness or depth ofregion 28. Such latter implanting will focus most of the implant towithin region 28, but perhaps not necessarily only place the impurityinto the changed outer portion.

Regardless, such implanting further adversely modifies or changes theexposed semiconductive material such that selectivity in the subsequentetch utilizing at least the tetramethyl ammonium hydroxide solution canbe substantially increased, such as to a selective etch ratio of 100:1.FIG. 7 illustrates such a subsequent etch removing material of regions28 and 30 selectively relative to semiconductive material therebeneathof region 20 which is substantially unchanged by either of the contactopening 26 etch or the exemplary subsequent ion implant. An exemplarydepth to the base of the source/drain diffusion regions is 2000Angstroms, with an example depth to the base of region 30 being 1000Angstroms. An example etch with a 2% by weight solution of tetramethylammonium hydroxide for 90 seconds at a temperature of 30° C. and ambientpressure produced a 1000 Angstroms selective removal of the damagedsilicon to the base of region 30.

Referring to FIG. 8, a conductive layer 32 is subsequently formed withinand over contact opening 32 and ideally in contact with diffusion region20.

Another alternate embodiment is described with reference to FIGS. 9 and10. Like numerals from the FIGS. 2-8 embodiments are utilized whereappropriate, with differences being indicated by the suffix “b” or withdifferent numerals. FIG. 9 illustrates a wafer fragment 40 b at aprocessing step immediately subsequent to processing of wafer 40 asdepicted in FIG. 4. In FIG. 9, a conductivity enhancing impurity hasbeen implanted into semiconductive material of diffusion region 20 afterhaving etched changed outer portion 28 to form region 30 b. Such isideally a shallow buried contact implant intended to enhanceconductivity of the contact, like the implant 30 of the second describedembodiment. Although the implant produced will have some effect inadversely modifying conductive properties of the silicon at the contact,such does not produce the double-damage effect in the contact of theprior art due to both remaining silicon damage from the dry etch to formthe contact and a subsequent buried contact implant.

Referring to FIG. 10, a conductive layer 32 is subsequently formedwithin and over contact opening 32 and ideally in contact with diffusionregion 20.

Yet another alternate embodiment is depicted in FIG. 11. Like numeralsfrom the FIGS. 2-10 embodiments are utilized where appropriate, withdifferences being indicated with the suffix “c” or with differentnumerals. FIG. 11 depicts a wafer fragment 40 c at a processing stepimmediately subsequent to that depicted with wafer 40 a in FIG. 7.Accordingly, wafer fragment 40 c has previously been processed by an ionimplant immediately prior to etching the changed outer portion, ideallyto enhance selectivity in the resulting etch of the damaged siliconrelative to undamaged silicon therebeneath. Further in FIG. 11, asubsequent buried contact conductivity enhancing ion implant isconducted to form region 50 within diffusion region 20.

In compliance with the statute, the invention has been described inlanguage .more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A method of forming an electrical contact tosemiconductive material comprising: forming an insulative layer over acontact area of semiconductive material; etching a contact openingthrough the insulative layer to the semiconductive material contactarea, said contact etching changing an outer portion of thesemiconductive material exposed by the contact etching; first implantinga conductivity enhancing impurity into the changed outer portion throughthe contact opening; after the first implanting, etching the changedouter portion of the semiconductive material through the contact openingsubstantially selective relative to semiconductive material therebeneathwhich is unchanged; after etching the changed outer portion, secondimplanting a conductivity enhancing impurity into the semiconductivematerial through the contact opening; and after the second implanting,forming conductively doped semiconductive material within the contactopening in contact with semiconductive material which is unchanged fromsaid contact opening etching.
 2. The method of claim 1 wherein etchingof the changed outer portion is conducted to etch all exposed changedouter portion material.
 3. The method of claim 1 wherein the etching ofthe changed outer portion is conducted using an etch chemistry whichetches the changed outer portion selective to semiconductive materialtherebeneath which is unchanged, and etching such changed outer portionuntil said semiconductive material therebeneath which is unchanged isoutwardly exposed.
 4. The method of claim 1 wherein the outer portionetching comprises wet etching with a basic solution.
 5. The method ofclaim 1 wherein said contact etching changes a physical property of theouter portion of the semiconductive material exposed by the contactetching.
 6. The method of claim 1 wherein the outer portion etchingcomprises wet etching with a tetramethyl ammonium hydroxide solution. 7.The method of claim 1 wherein the outer portion etching comprises wetetching with a tetramethyl ammonium hydroxide solution comprising fromabout 0.5% to 10% tetramethyl ammonium hydroxide by weight.
 8. Themethod of claim 1 comprising forming the contact opening with allelectrically conductive material therein to be void of silicide.
 9. Themethod of claim 1 wherein the conductive material comprises conductivelydoped semiconductive material formed in contact with semiconductivematerial unchanged by said contact etching.
 10. The method of claim 1wherein the first implanting is conducted to substantially only placethe impurity into the changed outer portion.
 11. The method of claim 1wherein the changed outer portion has a thickness, and the firstimplanting is conducted to place peak concentration of the implantsubstantially central relative to the thickness of the changed portion.12. A method of forming an electrical contact to semiconductive materialcomprising: forming an electrically conductive device over asemiconductive substrate, the semiconductive substrate having a contactarea proximate to the device; forming a first insulative layer over atleast a portion of the conductive device; forming a second insulativelayer over the first insulative layer and over the contact area; etchinga contact opening through the second insulative layer to the contactarea, said contact etching changing an outer portion of semiconductivematerial within the contact area exposed by the contact etching;implanting a conductivity enhancing impurity into the changed outerportion through the contact opening; after the implanting, etching thechanged outer portion of the semiconductive material within the contactarea through the contact opening substantially selective relative tosemiconductive material within the contact area therebeneath which isunchanged; and after etching the changed outer portion, formingconductive material within the contact opening in electrical connectionwith semiconductive material of the contact area.
 13. The method ofclaim 12 wherein the semiconductive material to which the conductivematerial within the contact opening ultimately electrically connectscomprises a conductive diffusion region formed within the semiconductivesubstrate.
 14. The method of claim 12 wherein the semiconductivematerial to which the conductive material within the contact openingultimately electrically connects comprises a conductive diffusion regionformed within the semiconductive substrate, the contact opening etchedto the contact area being substantially centrally located relative tothe diffusion region.
 15. The method of claim 12 wherein the outerportion etching comprises wet etching with a basic solution.
 16. Themethod of claim 12 wherein the outer portion etching comprises wetetching with a tetramethyl ammonium hydroxide solution.
 17. The methodof claim 12 wherein the outer portion etching comprises wet etching witha tetramethyl ammonium hydroxide solution comprising from about 0.5% to10% tetramethyl ammonium hydroxide by weight.
 18. The method of claim 12comprising forming the contact opening with all electrically conductivematerial therein to be void of silicide.
 19. The method of claim 12wherein the conductive material comprises conductively dopedsemiconductive material formed in contact with semiconductive materialunchanged by said contact etching.
 20. The method of claim 12 whereinsaid contact etching changes a physical property of the outer portion ofthe semiconductive material exposed by the contact etching.